Satellite DNA's and other simple, tandemly-repeated nucleotide sequences, are present in or about the centromeric, heterochromatic region of the chromosomes of man, and numerous other eukaryotes. Their functions are unknown. We seek support to continue our studies of satellite DNA's in Drosophila. We will employ established biochemical, genetic, and cytological procedures to extend our investigation of satellite DNA's. The proposed experiments may provide information about: 1) the arrangement of satellite DNA sequences along the chromosome; 2) the normal array of chromosomal proteins associated with sites rich in satellite DNA; #) the extent to which individual forms of satellite DNA evolve during speciation. Since satellite DNA's are a chromosomal feature common to Drosophila and to man, there is an excellent possibility that these experiments will provide information applicable to the problem of the organization and molecular architecture of human chromosomes.